Electrical machine

ABSTRACT

An electrical machine, in particular an alternator, is provided that has a shaft ( 13 ) that is held in at least one movable bearing point ( 25 ) by at least one bearing ( 19 ) in a hub ( 22 ). A metal sliding element ( 28 ) is fixed on the hub side between the bearing ( 19 ) and the hub ( 22 ).

BACKGROUND INFORMATION

An electrical machine is made known in DE 89 11 295 4 U1, in which ashaft is supported in a hub of a housing by a movable bearing. A slidingelement is fixed on the hub side between the bearing and the hub. Thesliding element permits the bearing to slide in the hub when the shaftundergoes thermally-induced changes in length and compensates fortemperature fluctuations and, therefore, changes in play in the hub. Thedisadvantage of this prior art is that the sliding ring or slidingelement made of plastic is inadequately resistant to operation-inducedstress on the movable bearing, so the play of the bearing inadvertentlyincreases, and increases even further due to magnetic forces. The stresson the bearing is therefore increased beyond the tolerable level.

ADVANTAGES OF THE INVENTION

The electrical machine having the features of the main claim has theadvantage that, due to the metallic sliding element, it has highhardness, which greatly limits the wear on the sliding element and alsoensures high dimensional stability of the sliding element, the supportis particularly reliable and particularly long-lasting. Due to themeasures listed in the subclaims, advantageous further developments ofthe electrical machine according to the main claim are possible. Aparticularly high dimensional stability results because the slidingelement has a minimum hardness of 570 HV 10.

The sliding element is particularly easy to manufacture because it isannular in shape. If a generally tubular sleeve abuts the slidingelement that is joined with this sliding element, it is possible toencapsulate the collector-ring space using this sliding element and itstubular sleeve part. Encapsulating the collector-ring space makes itpossible to seal out detrimental environmental influences, such as dust,humidity and wetness. According to a further embodiment, it is providedthat the sleeve part is joined with the sliding ring using aconnecting-element arrangement. This connecting-element arrangement hasthe advantage that it enables a reliable connection between the slidingring and the sleeve part. A particularly favorable and reliableconnection between the sliding ring and the sleeve part is obtainedusing a connecting-element arrangement configured with snap-on elements.A further reliable method of connecting the sleeve part with the slidingring in functionally secure fashion is to integrally extrude the sleevepart, which is made of plastic, on the sliding ring using a plasticpressure-casting method.

Using the features of the coordinated claim, it is possible to provide asliding ring for installation in the hub of a rotating machine, wherebya tubular sleeve part abuts the metallic sliding element.

BRIEF DESCRIPTION OF THE DRAWING

An exemplary embodiment of an electrical machine according to theinvention and a sliding element according to the invention are shown inthe figures.

FIG. 1 is a sectional drawing of a partially abstract embodiment of anelectrical machine,

FIG. 2 is a sectional drawing of a sliding element according to theinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A partial sectional drawing of an electrical machine 10 is shown inFIG. 1. In addition to further parts that are not shown nor essential tothe invention, electrical machine 10 has a shaft 13 on which anelectrically active rotor 16 is mounted. Shaft 13 is held by at leastone bearing 19 in a hub 22 composed of a metal alloy, e.g., an aluminumalloy. The support of shaft 13 of this hub 22 is configured as a“movable bearing point” 25. This movable bearing point 25 permits axialrelative movement between bearing 19 mounted on shaft 13 and hub 22. Asliding element 28 is inserted and fixed in the hub between bearing 19and hub 22, and the sliding element is composed of metal. Slidingelement 28 is fixed in hub 22 using a press fit. It is provided thatsliding element 28 has a minimum hardness of 570 HV 10. As indicated,the hardness is measured according to the Vickers hardness testingmethod. Ideally, the hardness is between 570 and 640 HV 10.

In order to maintain an even seat of bearing 19 in hub 22, it isprovided that sliding element 28 is configured as a ring.

A further exemplary embodiment of sliding element 28 is shown in FIG. 2.First of all, sliding element 28 has the annular shape mentionedpreviously and has a rotor side R and a collector-ring side S. Slidingelement 28 is joined with generally tubular sleeve part 31 that abutssliding element 28. The purpose of sleeve part 31 in electrical machine10 is to surround a sliding-contact device 34 and protect it fromdetrimental environmental influences.

Sleeve part 31 is joined with sliding element 28 by a connecting-elementarrangement 37. Connecting-element arrangement 37 includes a snap-onconnection shown in FIGS. 3 a and 3 b, for example, in which slidingelement 28 and sleeve part 31 each have snap-on elements 40 thatinteract with each other. On its collector-ring side, sliding element 28has an annular bead 43 and, abutting it axially in the direction towardthe rotor, an annular groove 46. Accordingly, sleeve part 31 has, on itsside closest to the rotor, an annular element 49 that extends radiallyinwardly and that axially abuts a radially outwardly extending annulargroove 52 in the direction toward the collector-ring side. As a result,sleeve part 31 and sliding element 28 are capable of being joined byengaging annular element 49 of sleeve part 31 in annular groove 46 ofsliding element 28. Conversely, annular bead 43 engages in annulargroove 52 of the sleeve element of sleeve part 31. In a furtherexemplary embodiment, it is provided that sleeve part 31 is integrallyextruded on sliding ring 28.

It is provided that sliding element 28 has positively-interlockingelements, as shown previously in FIG. 3 a. These positively-interlockingelements are previously-mentioned annular groove 46 and annular bead 42.By extrusion-coating these two elements, at least partially, a suitableconnection between sliding element 28 and sleeve part 31 is obtained.

As shown in FIG. 1, sleeve part 31 at least partially coverssliding-contact device 34 to provide current to rotor 16 and/orelectrical machine 10. An opening 55 is provided in the region ofsliding-contact device 34 on the periphery of the sleeve part 31, inwhich a brush holder 58 is insertable.

1. An electrical machine, in particular an alternator, with a shaft (13)that is held in at least one movable bearing point (25) by at least onebearing (19) in a hub (22), whereby a sliding element (28) is fixed onthe hub side between the bearing (19) and the hub (22), wherein thesliding element (28) is composed of metal.
 2. The electrical machine asrecited in claim 1, wherein the sliding element (28) has a minimumhardness of 570 HV
 10. 3. The electrical machine as recited in claim 1wherein the sliding element (28) is a ring.
 4. The electrical machine asrecited in claim 1 wherein a generally tubular sleeve part (31) abutsthe sliding element (28) and is joined with the sliding element.
 5. Theelectrical machine as recited in claim 4, wherein the sleeve part isjoined with the sliding element (28) by a connecting-element arrangement(37).
 6. The electrical machine as recited in claim 5, wherein theconnecting-element arrangement (37) is composed of snap-on elements(40).
 7. The electrical machine as recited in claim 4, wherein thesleeve part (31) is integrally extruded on the sliding element (28). 8.The electrical machine as recited in one claim 4 wherein the sleeve part(31) at least partially covers a sliding-contact device (34), and thereis an opening (55) in the region of the sliding-contact device (34), inwhich a brush holder is insertable.
 9. A sliding element forinstallation in the hub (22) of an electrical machine (10), wherein thesliding element (28) is metallic.
 10. The sliding element as recited inclaim 9, wherein a tubular sleeve part (31) abuts the sliding element(28).